The present invention relates to a two-sided surface grinding apparatus for grinding the opposite surfaces of thin sheet-like work, such as a semiconductor wafer.
As for a two-sided surface grinding apparatus for grinding the opposite surfaces of thin sheet-like work, such as a semiconductor wafer, there is a known one described, for example, in Japanese Patent Laid Open No. 2000-280155 gazette. The two-sided surface grinding apparatus described in Japanese Patent Laid Open No. 2000-280155 gazette comprises a pair of grinding whetstones rotatably supported with their grinding surfaces opposed to each other, a work rotation support means for supporting thin sheet-like work for rotation around the axis of a rotary shaft parallel with the rotary shaft of the grinding whetstones in such a state that at least part of each of the grinding subject surfaces on the opposite surfaces is disposed in the grinding position between the grinding surfaces of the grinding whetstones, and a pair of noncontact support means disposed in such a manner as to hold therebetween from opposite sides substantially the entire surface of a region outwardly of the grinding position in the grinding subject surfaces of the work and in such a manner as to noncontactly support the work by the pressure of a fluid, wherein the grinding subject surfaces on the opposite surfaces of the work are ground by rotating the work and the grinding whetstones with the work supported by the noncontact support means.
Further, in this two-sided surface grinding apparatus, the diameter of the grinding surfaces of the grinding whetstones is substantially equal to or somewhat greater than the radius of the work. That is, the relative positional relation between the grinding whetstones and the work is set such that the grinding surfaces of the grinding whetstones are always applied to the center of the grinding subject surfaces and part of the outer periphery of the work, thereby enabling the grinding whetstones to uniformly grind the entire surface of the work.
The noncontact support surfaces of the noncontact support means in this kind of two-sided surface grinding apparatus have been generally, for example, in the shape shown in FIG. 15. That is, an arcuate notch 111 is formed which extends from the substantially circular outer edge thereof at least over the central position B of work, with a grinding whetstone 112 disposed in this notch 111. Further, disposed in the noncontact support surfaces are a plurality of pockets 113 formed as recesses of substantially uniform depth, the arrangement being such that fluid, such as water, is discharged from fluid supply holes (illustration omitted) formed in the inner walls of these pockets 113.
Further, the pockets 113 are radially disposed in a plurality of rows (two rows in this case) so that they are substantially concentric circles with respect to the work center B. That is, a netlike mesh section 114 forming banks around the peripheries of the pockets 113 is composed of peripheral edges 114a disposed along the outer periphery of the noncontact support surfaces, and inside veins 114b disposed so as to divide the region inwardly of the peripheral edges 114a into a plurality of sections and connected to the peripheral edges 114a in a plurality of inside-and-outside connecting sections 115.
In the case of grinding the opposite surface of a wafer (for example, having a diameter of about 300 mm) by using a conventional two-sided surface grinding apparatus mentioned above, the wafer surfaces after grinding, as is known, have produced undulations of not more than μm order in concentric circles (hereinafter referred to simply as undulations) outwardly of the surfaces; however, such slight amount of undulations has heretofore caused no particular problem.
However, in recent years micronization of patterns to be formed on wafer surfaces has advanced, followed by the focal depth of exposure devices becoming very shallow, thus demanding a higher level for the flatness of the wafer surfaces, thus bringing about a situation in which even the undulations of not more than μm mentioned above can no longer be ignored.
With such conventional problems in mind, the present invention has for its object the provision of a two-sided surface grinding apparatus capable of eliminating the undulations of concentric circles produced on the work surface by grinding, thereby further improving the flatness of the work surfaces after grinding.